The present invention is directed to a wrapper for a smoking article, particularly for self-extinguishing cigarettes, formed of cellulose containing filler material and possibly burn promoting salts.
The dangers arising from smoking articles which are carelessly thrown away or which burn unobserved are well known. Both property insurance and life insurance statistics clearly underscore this fact. As a result, there has been no lack of attempts to produce smoking articles which extinguish themselves after a certain period of time.
In Patent Document EP-A-133 575, a cigarette is disclosed whose tobacco tube is wrapped with two different papers. Both papers are formed of cellulose and have approximately the same area weight of 20 to 25 g/m.sup.2. The porosity of the inner paper is approximately 1 CU (Coresta Unit) and the porosity of the outer paper is approximately 55 CU. The inner paper is filled with 14 percent by weight titanium dioxide and the outer paper is filled with 30 percent by weight calcium carbonate and, in addition, has 6 percent by weight anhydrous potassium citrate. The low porosity of the inner paper is obtained by coating or impregnating with suitable water-soluble, film-forming materials, for instance, methylcellulose, carboxymethylcellulose, starch, chemically modified starch, gum guar, sodium alginate, dextrin, gelatin and the like. A cigarette with such a wrapper is supposed to extinguish itself within a few minutes, after it comes into contact with objects, such as pillows, carpets, furniture, for limiting the free access of oxygen to the glowing end or tip of the cigarette.
In addition to the solution using two paper layers, EP-A-133 575 also describes a solution using only one paper layer. Again, this is a light weight paper layer of approximately 20 to 25 g/m.sup.2 area weight and a porosity of 1 to 4 CU, filled with titanium dioxide and/or calcium carbonate as filler material and 1.7 to 9 percent by weight anhydrous potassium citrate as a burn promoting salt.
Another advantageous feature of self-extinguishing smoking articles is that the so-called secondary smoke flow which stems from the glowing tip of the cigarette in the interval between draws on the cigarette is reduced. Secondary smoke flow is responsible, to a great extent, for so-called passive smoking. It would be desirable to suppress the formation of secondary smoke flow completely, however, its development is unavoidable, since smoking articles require a continuously burning glowing tip for readily appreciable reasons.
If the reduction of the secondary smoke flow is related to a reduction in the burning in the interval between two draws on a cigarette, this feature would be further advantageous in view of the rising prices of smoking articles.
Smoking articles with reduced secondary smoke flow enclosed or wrapped with two paper layers are known from the Patent Document DE-B-22 57 317. The inner layer is a highly porous cellulose fiber paper containing a finely powdered carbon, and alkali earth metal carbonates could also be added. The outer layer is a conventional cigarette paper. The inner layer, filled with carbon, may be glued so it can be held by the outer layer. In this known arrangement, the carbon in the inner paper layer absorbs the secondary smoke flow so that it is not visible without slowing down the burning of the tobacco.
Smoking articles, such as cigarettes, where the wrapper is a paper layer coated on the side facing the tobacco with a material for preventing the penetration of condensate or tar and the resultant formation of brown spots, is known from the Patent Document GB-A-21 43 150. Ethylene vinyl acetate (EVA), polyvinyl acetate (PVA), polyvinyl alcohol (PVOH), carboxymethylcellulose (CMC), starch and nitrocellulose lacquer are suggested as the coating.
It has also been suggested to coat the paper with metal for the same purpose. One suggestion is to attach a low-melting point plastic foil under the paper wrapper.
In Pat. Document DE-A-37 21 204, cigarette papers are known containing a substantially water-insoluble and thermally resistant filler material in the cellulose starting material. Under smoking conditions, such filler material affords a surface in the web of at least 80 m.sup.2 per square meter of the web and contains approximately 15 percent by weight of an alkali metal salt. The porosity is in the range of 5 to 30 CU.
Finally, a cigarette is known from U.S. Pat. No. 3,633,589 which is wrapped with two paper layers. The cover layer is a conventional porous cigarette paper with good burning characteristics and ash qualities. The inner layer is a practically non-porous paper. The inner layer burns more slowly than the cover layer and the tobacco. Accordingly, air must pass completely through the glowing cigarette tip at each draw. As a result, the main smoke flow is supposed to contain less air, produce a rich, pure smoking sensation, and thereby reduce the tendency of the smoker to inhale. Secondary smoke flow or self-extinguishing are not mentioned in this patent.
Unfortunately, wrappers for smoking articles suggested in the literature are supposed to enable a reduction of the secondary smoke flow and/or self-extinguishing, however, they have not been successful in practice. Suggestions of the addition of certain chemicals to the cigarette paper resulted in an adulteration of the tobacco taste. Moreover, decomposition products which are objectionable with respect to health occur in certain of the proposals.
In other instances, the wrappers have a visually unattractive appearance, either because they are colored gray or brown, or form gray or even black ashes, since no closed ash tube is formed and/or because condensate or tar penetrate and form unsightly brown spots.
Higher prices discourage the use of two different paper layers as the wrapper, because each smoking article must pass through a second processing step. Further, there is the risk that the outer layer will become detached from the inner layer, and the inner layer usually has an unattractive and artificial look because of its filler material contents and other chemicals which become visible and, as experience has shown, leads to rejection by the consumer.